Conventionally, there is known a power transmission device for a hybrid vehicle including an engine and a power distribution mechanism (a planetary gear mechanism) in which two rotary machines are connected. In a hybrid system including such a power transmission device, a rotation shaft of an engine, a rotation shaft of a first rotary machine, a rotation shaft of a second rotary machine, and a drive wheel are respectively connected to rotation components of the power distribution mechanism. Patent Literature 1 below discloses a structure in which an engine, a first electric generator, a second electric generator, and a drive wheel are respectively and individually connected to rotation components of a power distribution mechanism. In the hybrid system of Patent Literature 1, a friction clutch and a one-way clutch are interposed between the engine and the power distribution mechanism.